1 //===- DominatorSet.cpp - Dominator Set Calculation --------------*- C++ -*--=//
3 // This file provides a simple class to calculate the dominator set of a method.
5 //===----------------------------------------------------------------------===//
7 #include "llvm/Analysis/Dominators.h"
8 #include "llvm/Analysis/SimplifyCFG.h" // To get cfg::UnifyAllExitNodes
9 #include "llvm/Support/DepthFirstIterator.h"
10 #include "llvm/Support/STLExtras.h"
11 #include "llvm/Method.h"
14 //===----------------------------------------------------------------------===//
16 //===----------------------------------------------------------------------===//
18 // set_intersect - Identical to set_intersection, except that it works on
19 // set<>'s and is nicer to use. Functionally, this iterates through S1,
20 // removing elements that are not contained in S2.
22 template <class Ty, class Ty2>
23 void set_intersect(set<Ty> &S1, const set<Ty2> &S2) {
24 for (typename set<Ty>::iterator I = S1.begin(); I != S1.end();) {
27 if (!S2.count(E)) S1.erase(E); // Erase element if not in S2
31 //===----------------------------------------------------------------------===//
32 // DominatorBase Implementation
33 //===----------------------------------------------------------------------===//
35 bool cfg::DominatorBase::isPostDominator() const {
36 // Root can be null if there is no exit node from the CFG and is postdom set
37 return Root == 0 || Root != Root->getParent()->front();
41 //===----------------------------------------------------------------------===//
42 // DominatorSet Implementation
43 //===----------------------------------------------------------------------===//
45 // DominatorSet ctor - Build either the dominator set or the post-dominator
46 // set for a method...
48 cfg::DominatorSet::DominatorSet(const Method *M) : DominatorBase(M->front()) {
49 calcForwardDominatorSet(M);
52 // calcForwardDominatorSet - This method calculates the forward dominator sets
53 // for the specified method.
55 void cfg::DominatorSet::calcForwardDominatorSet(const Method *M) {
56 assert(Root && M && "Can't build dominator set of null method!");
57 assert(Root->use_size() == 0 && "Root node has predecessors in method!");
62 DomSetType WorkingSet;
63 df_iterator<const Method*> It = df_begin(M), End = df_end(M);
64 for ( ; It != End; ++It) {
65 const BasicBlock *BB = *It;
66 BasicBlock::pred_const_iterator PI = BB->pred_begin(),
67 PEnd = BB->pred_end();
68 if (PI != PEnd) { // Is there SOME predecessor?
69 // Loop until we get to a predecessor that has had it's dom set filled
70 // in at least once. We are guaranteed to have this because we are
71 // traversing the graph in DFO and have handled start nodes specially.
73 while (Doms[*PI].size() == 0) ++PI;
74 WorkingSet = Doms[*PI];
76 for (++PI; PI != PEnd; ++PI) { // Intersect all of the predecessor sets
77 DomSetType &PredSet = Doms[*PI];
79 set_intersect(WorkingSet, PredSet);
83 WorkingSet.insert(BB); // A block always dominates itself
84 DomSetType &BBSet = Doms[BB];
85 if (BBSet != WorkingSet) {
86 BBSet.swap(WorkingSet); // Constant time operation!
87 Changed = true; // The sets changed.
89 WorkingSet.clear(); // Clear out the set for next iteration
94 // Postdominator set constructor. This ctor converts the specified method to
95 // only have a single exit node (return stmt), then calculates the post
96 // dominance sets for the method.
98 cfg::DominatorSet::DominatorSet(Method *M, bool PostDomSet)
99 : DominatorBase(M->front()) {
100 if (!PostDomSet) { calcForwardDominatorSet(M); return; }
102 Root = cfg::UnifyAllExitNodes(M);
103 if (Root == 0) { // No exit node for the method? Postdomsets are all empty
104 for (Method::iterator MI = M->begin(), ME = M->end(); MI != ME; ++MI)
105 Doms[*MI] = DomSetType();
113 set<const BasicBlock*> Visited;
114 DomSetType WorkingSet;
115 idf_iterator<const BasicBlock*> It = idf_begin(Root), End = idf_end(Root);
116 for ( ; It != End; ++It) {
117 const BasicBlock *BB = *It;
118 BasicBlock::succ_const_iterator PI = BB->succ_begin(),
119 PEnd = BB->succ_end();
120 if (PI != PEnd) { // Is there SOME predecessor?
121 // Loop until we get to a successor that has had it's dom set filled
122 // in at least once. We are guaranteed to have this because we are
123 // traversing the graph in DFO and have handled start nodes specially.
125 while (Doms[*PI].size() == 0) ++PI;
126 WorkingSet = Doms[*PI];
128 for (++PI; PI != PEnd; ++PI) { // Intersect all of the successor sets
129 DomSetType &PredSet = Doms[*PI];
131 set_intersect(WorkingSet, PredSet);
135 WorkingSet.insert(BB); // A block always dominates itself
136 DomSetType &BBSet = Doms[BB];
137 if (BBSet != WorkingSet) {
138 BBSet.swap(WorkingSet); // Constant time operation!
139 Changed = true; // The sets changed.
141 WorkingSet.clear(); // Clear out the set for next iteration
147 //===----------------------------------------------------------------------===//
148 // ImmediateDominators Implementation
149 //===----------------------------------------------------------------------===//
151 // calcIDoms - Calculate the immediate dominator mapping, given a set of
152 // dominators for every basic block.
153 void cfg::ImmediateDominators::calcIDoms(const DominatorSet &DS) {
154 // Loop over all of the nodes that have dominators... figuring out the IDOM
157 for (DominatorSet::const_iterator DI = DS.begin(), DEnd = DS.end();
159 const BasicBlock *BB = DI->first;
160 const DominatorSet::DomSetType &Dominators = DI->second;
161 unsigned DomSetSize = Dominators.size();
162 if (DomSetSize == 1) continue; // Root node... IDom = null
164 // Loop over all dominators of this node. This corresponds to looping over
165 // nodes in the dominator chain, looking for a node whose dominator set is
166 // equal to the current nodes, except that the current node does not exist
167 // in it. This means that it is one level higher in the dom chain than the
168 // current node, and it is our idom!
170 DominatorSet::DomSetType::const_iterator I = Dominators.begin();
171 DominatorSet::DomSetType::const_iterator End = Dominators.end();
172 for (; I != End; ++I) { // Iterate over dominators...
173 // All of our dominators should form a chain, where the number of elements
174 // in the dominator set indicates what level the node is at in the chain.
175 // We want the node immediately above us, so it will have an identical
176 // dominator set, except that BB will not dominate it... therefore it's
177 // dominator set size will be one less than BB's...
179 if (DS.getDominators(*I).size() == DomSetSize - 1) {
188 //===----------------------------------------------------------------------===//
189 // DominatorTree Implementation
190 //===----------------------------------------------------------------------===//
192 // DominatorTree dtor - Free all of the tree node memory.
194 cfg::DominatorTree::~DominatorTree() {
195 for (NodeMapType::iterator I = Nodes.begin(), E = Nodes.end(); I != E; ++I)
200 cfg::DominatorTree::DominatorTree(const ImmediateDominators &IDoms)
201 : DominatorBase(IDoms.getRoot()) {
202 const Method *M = Root->getParent();
204 Nodes[Root] = new Node(Root, 0); // Add a node for the root...
206 // Iterate over all nodes in depth first order...
207 for (df_iterator<const Method*> I = df_begin(M), E = df_end(M); I != E; ++I) {
208 const BasicBlock *BB = *I, *IDom = IDoms[*I];
210 if (IDom != 0) { // Ignore the root node and other nasty nodes
211 // We know that the immediate dominator should already have a node,
212 // because we are traversing the CFG in depth first order!
214 assert(Nodes[IDom] && "No node for IDOM?");
215 Node *IDomNode = Nodes[IDom];
217 // Add a new tree node for this BasicBlock, and link it as a child of
219 Nodes[BB] = IDomNode->addChild(new Node(BB, IDomNode));
224 void cfg::DominatorTree::calculate(const DominatorSet &DS) {
225 Nodes[Root] = new Node(Root, 0); // Add a node for the root...
227 if (!isPostDominator()) {
228 // Iterate over all nodes in depth first order...
229 for (df_iterator<const BasicBlock*> I = df_begin(Root), E = df_end(Root);
231 const BasicBlock *BB = *I;
232 const DominatorSet::DomSetType &Dominators = DS.getDominators(BB);
233 unsigned DomSetSize = Dominators.size();
234 if (DomSetSize == 1) continue; // Root node... IDom = null
236 // Loop over all dominators of this node. This corresponds to looping over
237 // nodes in the dominator chain, looking for a node whose dominator set is
238 // equal to the current nodes, except that the current node does not exist
239 // in it. This means that it is one level higher in the dom chain than the
240 // current node, and it is our idom! We know that we have already added
241 // a DominatorTree node for our idom, because the idom must be a
242 // predecessor in the depth first order that we are iterating through the
245 DominatorSet::DomSetType::const_iterator I = Dominators.begin();
246 DominatorSet::DomSetType::const_iterator End = Dominators.end();
247 for (; I != End; ++I) { // Iterate over dominators...
248 // All of our dominators should form a chain, where the number of
249 // elements in the dominator set indicates what level the node is at in
250 // the chain. We want the node immediately above us, so it will have
251 // an identical dominator set, except that BB will not dominate it...
252 // therefore it's dominator set size will be one less than BB's...
254 if (DS.getDominators(*I).size() == DomSetSize - 1) {
255 // We know that the immediate dominator should already have a node,
256 // because we are traversing the CFG in depth first order!
258 Node *IDomNode = Nodes[*I];
259 assert(IDomNode && "No node for IDOM?");
261 // Add a new tree node for this BasicBlock, and link it as a child of
263 Nodes[BB] = IDomNode->addChild(new Node(BB, IDomNode));
269 // Iterate over all nodes in depth first order...
270 for (idf_iterator<const BasicBlock*> I = idf_begin(Root), E = idf_end(Root);
272 const BasicBlock *BB = *I;
273 const DominatorSet::DomSetType &Dominators = DS.getDominators(BB);
274 unsigned DomSetSize = Dominators.size();
275 if (DomSetSize == 1) continue; // Root node... IDom = null
277 // Loop over all dominators of this node. This corresponds to looping
278 // over nodes in the dominator chain, looking for a node whose dominator
279 // set is equal to the current nodes, except that the current node does
280 // not exist in it. This means that it is one level higher in the dom
281 // chain than the current node, and it is our idom! We know that we have
282 // already added a DominatorTree node for our idom, because the idom must
283 // be a predecessor in the depth first order that we are iterating through
286 DominatorSet::DomSetType::const_iterator I = Dominators.begin();
287 DominatorSet::DomSetType::const_iterator End = Dominators.end();
288 for (; I != End; ++I) { // Iterate over dominators...
289 // All of our dominators should form a chain, where the number of elements
290 // in the dominator set indicates what level the node is at in the chain.
291 // We want the node immediately above us, so it will have an identical
292 // dominator set, except that BB will not dominate it... therefore it's
293 // dominator set size will be one less than BB's...
295 if (DS.getDominators(*I).size() == DomSetSize - 1) {
296 // We know that the immediate dominator should already have a node,
297 // because we are traversing the CFG in depth first order!
299 Node *IDomNode = Nodes[*I];
300 assert(IDomNode && "No node for IDOM?");
302 // Add a new tree node for this BasicBlock, and link it as a child of
304 Nodes[BB] = IDomNode->addChild(new Node(BB, IDomNode));
314 //===----------------------------------------------------------------------===//
315 // DominanceFrontier Implementation
316 //===----------------------------------------------------------------------===//
318 const cfg::DominanceFrontier::DomSetType &
319 cfg::DominanceFrontier::calcDomFrontier(const DominatorTree &DT,
320 const DominatorTree::Node *Node) {
321 // Loop over CFG successors to calculate DFlocal[Node]
322 const BasicBlock *BB = Node->getNode();
323 DomSetType &S = Frontiers[BB]; // The new set to fill in...
325 for (BasicBlock::succ_const_iterator SI = BB->succ_begin(),
326 SE = BB->succ_end(); SI != SE; ++SI) {
327 // Does Node immediately dominate this successor?
328 if (DT[*SI]->getIDom() != Node)
332 // At this point, S is DFlocal. Now we union in DFup's of our children...
333 // Loop through and visit the nodes that Node immediately dominates (Node's
334 // children in the IDomTree)
336 for (DominatorTree::Node::const_iterator NI = Node->begin(), NE = Node->end();
338 DominatorTree::Node *IDominee = *NI;
339 const DomSetType &ChildDF = calcDomFrontier(DT, IDominee);
341 DomSetType::const_iterator CDFI = ChildDF.begin(), CDFE = ChildDF.end();
342 for (; CDFI != CDFE; ++CDFI) {
343 if (!Node->dominates(DT[*CDFI]))
351 const cfg::DominanceFrontier::DomSetType &
352 cfg::DominanceFrontier::calcPostDomFrontier(const DominatorTree &DT,
353 const DominatorTree::Node *Node) {
354 // Loop over CFG successors to calculate DFlocal[Node]
355 const BasicBlock *BB = Node->getNode();
356 DomSetType &S = Frontiers[BB]; // The new set to fill in...
359 for (BasicBlock::pred_const_iterator SI = BB->pred_begin(),
360 SE = BB->pred_end(); SI != SE; ++SI) {
361 // Does Node immediately dominate this predeccessor?
362 if (DT[*SI]->getIDom() != Node)
366 // At this point, S is DFlocal. Now we union in DFup's of our children...
367 // Loop through and visit the nodes that Node immediately dominates (Node's
368 // children in the IDomTree)
370 for (DominatorTree::Node::const_iterator NI = Node->begin(), NE = Node->end();
372 DominatorTree::Node *IDominee = *NI;
373 const DomSetType &ChildDF = calcPostDomFrontier(DT, IDominee);
375 DomSetType::const_iterator CDFI = ChildDF.begin(), CDFE = ChildDF.end();
376 for (; CDFI != CDFE; ++CDFI) {
377 if (!Node->dominates(DT[*CDFI]))